The solid-state starting device of AC motors, in the prior art, adopts a starting method through anti-parallel thyristor bidirectional valves which can decrease the voltage applied to the motor. Due to the square of the voltage being directly proportional to the torque of the motor, the starting torque is very small but the impact current is very strong, normally being controlled at 4-6 times of the rated current of the motor, which can easily result in abnormal operation occurring, such as block-up or unsuccessful starting. In addition, use of such conventional adjustable-speed equipment is very costly.